Metal roof structures typically comprise a series of parallel rafter beams extending across the building in one direction and purlin beams parallel to each other mounted on top of the rafters extending in a direction normal to the rafters. Insulation material in long sheets is placed in the area between purlins. The sheets of insulation material can be laid along the length of the purlins or across the purlins in a direction normal to the purlins. If desired, the roof structure can have a first layer of insulation material which is laid along the length of the purlins, and a second layer of insulation material which is laid laterally across the purlins on top of the first layer on insulation. Hard roofing material such as metal decking is then attached on top of the purlins over the insulation material. Because the hard roofing material comes in long sheets and the roofs generally have two sloped sections, it is customary to construct the roof along the length of the structure from one end to the other. The workers stand on the previously laid section of roof to construct the next section.
Some roof structures have bracing or sag rods extending between adjacent purlins to provide rigidity to the purlin beams. The bracing includes elongated bars or straps which are fastened to adjacent purlins. The bracing is commonly attached to the vertical portions of the purlins and can extend from the bottom of one purlin to the top of an adjacent purlin. Thus, bracing provides a certain amount of rigidity to the roof structure so that purlins do not bend or twist with respect to one another. Although bracing can provide rigidity to the purlins, the presence of the bracing can interfere with the insulation material placed in the space between the purlins. The insulation material may be compressed around the regions of the bracing, thereby reducing the overall thermal or R value of the roof structure. In a roof structure in which the hard roofing material is directly fastened to the purlins, the bracing generally no longer serves the purpose of providing required rigidity to the purlins in the final roof structure. The cooperation of the attached hard roofing material, purlins, and rafter beams provides for a relatively strong structure, wherein the purlins are unlikely to bend or deform. Thus, for these types of roof structures, the bracing mainly provides support during construction of the roof.
The insulation material is supported between the purlins beneath the hard roofing material. Various methods of supporting the insulation material have been used. Mounting straps or wire mesh which are attached to or draped over the purlins forming a lattice have been used. A sheet, typically made of vinyl and acting as a vapor barrier, is then rolled onto the lattice, and insulation material is placed between adjacent purlins and over the sheet. If the installation of the lattice is done from underneath the roof structure, scaffolding or lifting equipment is typically required for installation. Since the lattice encompasses the entire roof, installation is costly and time consuming. Once the hard roofing material is mounted on the purlins, the sheet can support the insulation material and the lattice no longer serves any useful purpose.
Some systems dispense with the lattice and use the sheet itself to support the insulation material. The support sheet is dispensed from a roll and draped from adjacent purlins. Insulation material is then placed on top of the support sheet. A carriage has been used to aid in the dispensing of the support sheet, such as that disclosed in U.S. Pat. No. 4,967,535 to Alderman. The carriage is positioned on top of the purlins and travels the length of the purlins during the roof construction. A roll of the support sheet material is mounted on the carriage and the support sheet is dispensed from the roll and placed on top of the purlins. As the carriage travels the length of the purlins, the support sheet is draped across the purlins.
The purlin beams, which are mounted on and positioned above the rafter beams, can have various cross-sectional shapes, but typically have a Z-shaped or I-shaped cross-section. In some instances due to the weight of the workers standing on a completed section of the roof or due to the weight of the carriage, the purlins can be bent or deformed from their original shape to a deformed shape. For example, a Z-shaped purlin generally has a planar upper horizontal portion which is perpendicular to a planar vertical web which is perpendicular to a planar lower horizontal portion when the Z-shaped purlin is in an original position. The Z-shaped purlin may be deformed such that the angle between the upper horizontal portion and the vertical web and the angle between the vertical web and the lower horizontal portion are each greater than 90 degrees such that the vertical web is no longer oriented in a vertical plane. Thus, the purlin has a slanted Z-shaped cross-section. Deformed purlins are undesirable due to complications which can arise when the sheets of hard roofing material are fastened to the purlins.
It would be desirable to have an apparatus and method of straightening purlins of a roof structure which have been deformed from an original position to a deformed position which is inexpensive and simple to perform., and which may eliminate the need for extensive bracing.